One component used in integrated circuitry is a capacitor. Such a component includes at least two electrical conductors separated by a dielectric. Energy may be electrostatically stored in an electric field within the dielectric.
Memory is one type of integrated circuitry which may include capacitors. Memory may be fabricated in one or more arrays of individual memory cells. Memory cells may be written to, or read from, using digit lines (which may also be referred to as bit lines, data lines, sense lines, or data/sense lines) and access lines (which may also be referred to as word lines). The digit lines may conductively interconnect memory cells along columns of the array, and the access lines may conductively interconnect memory cells along rows of the array. Each memory cell may be uniquely addressed through the combination of a digit line and an access line.
Memory cells may be volatile or non-volatile. Non-volatile memory cells can store data for extended periods of time, in many instances including when the computer is turned off. Volatile memory dissipates and therefore requires being refreshed/rewritten, in many instances multiple times per second. Regardless, memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
One type of non-volatile memory is ferroelectric random access memory (FeRAM). Individual memory cells in FeRAM may include a ferroelectric capacitor. These capacitors have ferroelectric dielectric material as at least part of the capacitor dielectric. Ferroelectric materials exhibit a spontaneous electric polarization that can be reversed by the application of an external electric field. In a ferroelectric material, polarization occurs in accordance with a suitable applied voltage between two electrodes, and such polarization remains after the applied voltage has been removed. The polarization can be reversed by application of a suitable inverted voltage. Each polarization state has different capacitance from the other, and which ideally can be used to store and read a memory state without reversing the polarization state until such is desired to be changed. FeRAM memory cells incorporating a ferroelectric capacitor are thereby non-volatile due to the bi-stable characteristics of the ferroelectric material that forms a part of the capacitor. Ferroelectric capacitors may also be used in integrated circuitry other than memory.
Properties associated with ferroelectric capacitors include endurance (how many programmed cycle changes can occur before device failure), retention (maintaining a programmed state without an un-programmed state change), and imprint (becoming resistive to programmed polarization reversal evidenced by a lateral shift of the hysteresis loop). Accordingly, it is desirable to have high endurance, high retention, and low imprint in ferroelectric capacitors.